While this repair is specific to the Acu-Rite 300s Digital Readout (DRO), it may be useful for other equipment that uses LCD displays.

Our DRO has been inconsistently dim and hard to read, getting worse over the past few months. This is often an indication of a bad CCFL (cold-cathode fluorescent lamp), commonly used for backlighting in (older) LCD displays. It is very costly to have the manufacturer repair a backlight on these DROs, but the actual CCFL is inexpensive and easily obtained (around $20 USD). This Instructables describes how to replace the CCFL backlight.

First, two notes. First, before doing anything, check to see if adjusting the contrast and brightness will help. On this DRO, both are set via software. (Check the manual for instructions, or see the last step of this for a condensed version.) Second, it may be possible to replace the CCFL with an LED equivalent. LEDs have much longer lifetimes than CCFL.

This procedure worked for us, but we can't guarantee that it will work for everyone. If the backlight repair goes horribly, a replacement LCD display is available for a little over $100 USD.

You'll probably want to do this in two stages--first, take the DRO apart to determine the display type (e.g., ours was a Hitachi SC14Q004) so you can order the correct CCFL (or LED!). Then complete the repair once you have the correct CCFL in hand.

This took us (with stops for photos--thanks Al!) way less than an hour.

Supplies

Replacement CCFL backlight lamp (e.g., for 5.7" Hitachi SC14Q004)

#2 Philips screwdriver

Torx 15 screwdriver

small flat-blade screwdriver

sharp knife (x-acto, scalpel, etc.)

pocket knife blade (might be able to use the x-acto from above)

strong double-stick foam tape or a good adhesive tape (we used 1/2" kapton)

Step 1: Open Case

Remove power cord and all other connections (e.g., glass scales).

Clean any dirt and chips from the outside and in the gap between front and back part of the enclosure.

Flip the case on a towel so you have access to the back.

Gently pry off the plastic curved pieces on either end. They'll pry up and then you can unclip them.

Then remove the 4 Philips screws using #2 screwdriver.

Step 2: Unscrew LCD Display

Carefully open the case, observing that several cables connect the two halves. When opened as shown in the photos, there won't be any stress on the cables.

Using a #2 Philips screwdriver, remove the 4 screws holding the LCD to the case.

Note that on our unit, the LCD details were on a small label in one corner.

Step 3: Detach Flat Cable From Back Shield

On our unit, the flat cable to the display was solidly attached to the back of the LCD display.

Being careful not to nick or cut the flat cable at all, cut through the double-stick tape with a sharp thin blade. Do not exert much force on the flat cable or bend it sharply.

Step 4: Loosen Front Shield

This LCD has two overlapping metal shields. The front shield is secured with little tabs that are bent to lock the shield in place. There are at least 6 of these that we need to move. Use a small screwdriver or needle-nose pliers to gently bend the tabs away.

Important note--the two tabs at the end with the exposed printed circuit board are soldered. Don't bother unsoldering these. We just need to get the front shield away enough to be able to remove the back shield (next step), so we can leave those tabs soldered.

Step 5: Remove Back Shield

Bend the front shield (loosened in the previous step) down at least 1/2" or so. (You may find you need to help two small "steps" in the shield move--they're in the two cavities where the LCD sits on the mounting bosses.)

This should expose 3 long horizontal tabs that hold the back shield in place--they're all along that one end. Carefully use a knife to release the tabs. You should be able to remove the back shield entirely once the tabs are released.

Step 6: Get Access to the CCFL

Gently remove the backlight from the display. It is a clear plastic block with plastic on both sides.

Gently peel back the translucent thin plastic from the thick clear plastic block. The CCFL tube is captured in the loop this makes at the end of the block. Try not to create any bends in the plastic, and work with clean hands.

Step 7: Place the New CCFL

The CCFL may be glass and may be fragile. Treat the old and new one gently.

The new CCFL will have the correct wire lengths and orientation of the end caps. Replace the old CCFL with the new one in the exact same orientation.

Fold and secure the translucent plastic sheet in place.

Step 8: Route the Wires Inside the Display

Use a small screwdriver to carefully route the wires in the channels provided. Note that the wire from the far end of the tube goes under the termination of the near end.

Re-assemble the display by first installing the back shield, attaching it using the 3 long tabs, and then the front shield using the 6 or so bent tabs.

Step 9: Secure the Flat Cable

Secure the flat cable to the display using good quality double-stick tape or something like 1/2" wide Kapton tape.

Step 10: Plug in the New CCFL

Follow the old CCFL wires to the 4-pin connector on the power supply. This connector has a locking tab to it--use a small screwdriver to pry the lock away from the connector as you gently remove the connector.

Plug in the new CCFL.

Use a Torx 15 bit to open the cable holder, remove the old CCFL wires, and install the new ones.

Step 11: Reassemble and Adjust Brightness and Contrast

Install the LCD using 4 short sheet metal screws. ("Pro-tip": with gentle downward pressure, turn the screws backwards until you feel them drop down--now screw forward. This should pick up the thread already in the plastic boss.)

Clean around the (red/orange) rubber seal, then carefully reassemble the case. Use 4 screws, then clip on the plastic clips.

Connect power cord and power on.

If the display is not great, don't panic. (And recall that it takes forever for the DRO to bootup.)

Use the right arrows to change the soft keys until you see "setup". Press that key.

Use the down arrow to select "console adjustment" and press the Enter key.

Use the up/down arrows to select brightness and contrast in turn, adjusting with the two left soft keys. Contrast especially should give great results.

Once you have the desired settings, press Enter to save, then "C" to return to normal operation.